Extreme low ambient temperatures, such as −30° C. (−22° F.) and below, for example, diminish the ability of a vehicle traction battery to deliver current to the motor of an electric or hybrid vehicle. Thermal conditioning of the battery improves performance in low ambient temperatures.
Various strategies have been used to provide battery thermal conditioning, many of which require external interfaces (electrical, fluid, or air) to warm the battery pack. One such method uses a positive thermal coefficient (PTC) resistive element disposed adjacent the outside of the battery in a position to heat the battery. This method requires a separate heater positioned to heat the battery and a PTC resistive element for each battery cell. Another strategy for heating a vehicle battery uses a secondary battery module having a housing that surrounds the battery to allow a heat transfer medium to flow in and out of the housing. This approach requires a large battery module and the use of a heat transfer medium. Another strategy includes a battery warmer having a positive temperature coefficient device attached to a side of the battery. Yet another approach includes an interior battery temperature sensor that controls current flow for a heating element secured to a cooling plate within the battery interior.